This invention relates to a device for tightening and adjusting a wind-around drive constructed as a chain by means of which a camshaft of an internal combustion engine drives a second camshaft.
U.S. Pat. No. 4 862 845 relates to a device for tightening and adjusting a chain which is operative between two camshafts of an internal-combustion engine, in which case the relative rotating position of the two camshafts with respect to one another is changed by adjusting the chain. On the one hand, this construction has the disadvantage that the adjusting operation partially takes place by means of high-expenditure gears which makes a largely no-delay change of the relative rotating position of the camshafts more difficult. In addition, for implementing the shown embodiments, comprehensive constructive and empirical tests are required which cause considerable expenses.
European Patent Document EP 0 445 356 A1 (corresponding to German Patent Document DE 40 06 910) discloses a device for tightening and adjusting a camshaft chain drive which comprises hydraulic pistons and which achieves good results with respect to its operation.
The German journals DE-Z ATZ Automobiltechnische Zeitschrift 93 (1991), Volume 10 and MTZ Motortechnische Zeitschrift 52 (1991), Volume 12, describe a camshaft adjustment with the characteristics of the above-mentioned European Patent Document EP 0 445 356. Accordingly, while the outlet camshaft is positioned in a constant manner, two positions of the inlet camshaft are implemented:
Power position (=initial position); late inlet device EM=120.degree., KW low valve overlap; PA1 Torque position; early inlet device EM=105.degree., KW larger valve overlap.
The results of this implemented device for the adjusting of camshafts with respect to power, torque, exhaust emissions and finally fuel consumption underline its targeted construction.
It is an object of the invention to further improve this device while maintaining its basic concept.
According to the invention, this object is achieved by providing an adjusting device for adjusting the position of one of the hydraulic pistons used to adjust the chain.
Principal advantages achieved by means of the invention are that, by means of the adjusting device, in addition to the late position--the basic control time--and the early position--the torque position--a central intermediate position can be selectively utilized.
By means of these three positions, a relatively large bandwidth can be implemented of variable valve timing with the existing engine oil pressure which is similar to a continuous or proportional adjustment, but without the constructional expenditures required for this purpose. These expenditures relate to the sensing system for the actual value detection of the camshaft, to a continuous electromagnetic valve and the holding of the adjuster piston in a defined position. For conventional systems--axial adjusters--additional high-expenditure high-performance oil pumps (&gt;20 bar) are required.
In preferred embodiments of the present invention, the adjusting device comprises another hydraulic piston which can be integrated teleologically at acceptable cost into the hydraulic system comprising two hydraulic pistons. The respective end stop for the third hydraulic piston can be integrated in a simple manner into the existing hydraulic system. Finally, the control of the hydraulic piston takes place in preferred embodiments of the invention by means of a 5/3-way valve which ensures a good as well as secure operation and, together with a lifting magnet actuating it, can be integrated in a simple manner into the housing of the hydraulic pistons.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.